A major hurdle to effective cancer treatmen relates to delivery of the therapeutic agent to the diseased tissue without adversely affecting normal cells. One approach that has proven effective is the use of folic acid as a targeting moiety. Many tumor types have been shown to overexpress folic acid receptors relative to normal cells. Thus, conjugation of folic acid to the chemotherapeutic agent of interest can result in efficient tumor localization, with those conjugates often entering the cell via receptor mediated endocytosis. Such "trojan horse" type delivery approaches may be particularly effective when faced with tumors displaying multi-drug resistance due to P-glycoprotein overexpression. Another hallmark of tumor proliferation is the upregulation of matrix metalloproteinases (MMPs), which are responsible for tissue remodeling during tumor growth. Recent studies have shown that this enzyme activity can be harnessed to create enzyme-dependent targeting moieties for neoplastic growths. Thus, the objective of this exploratory research proposal is to develop a new class of core/shell hydrogel particles (microgels) that will target and enter cancer cells via receptor mediated endocytosis, and then cause cell death by release of a therapeutic payload. Importantly, we will design these microgels to target the cancer cells only when specific MMP activity is present, thereby creating a vector that responds only when faced with multiple abnormal cellular conditions. Our central hypothesis is that core/shell hydrogel particles represent an innovative, effective, and highly versatile platform for such delivery vehicles. We have formulated this hypothesis as a result of studies that show that simple folate-modified core/shell microgels can enter cancer cells in culture and then undergo endosomal escape into the cytosol. We will attain our objectives via the following specific aims: Aim 1: To utilize doxorubicin-loaded, folate-modified, degradable core/shell microgels to target cells in vitro to specifically evade P-glycoprotein based multi-drug resistance; Aim 2: To develop multi-functional core/shell microgels that "display" folate in response to specific matrix metalloproteinase (MMP) activity. The outcomes of these efforts will be the development of a new class of delivery vehicles for anti-tumor agents, which will be poised for transfer to in vivo studies at the end of this grant period. We will also gain a detailed understanding of the fundamental issues involved in receptor-mediated endosomal uptake of polymeric nanoparticles. [unreadable] [unreadable] [unreadable]